This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-086993, filed Mar. 26, 2002, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a driving method and a driving apparatus for a display panel using an organic EL element. More particularly, in an organic EL matrix panel based on the multiple line driving method, a driving method is achieved which is capable of obtaining sufficient luminance necessary for the matrix panel and which improves the reliability of an organic EL element, without applying an excessive voltage for high duty drive to the organic EL element that forms pixels.
2. Description of the Related Art
The organic EL elements are now being commercialized as information displays having characteristics such as spontaneous light, high luminance, high efficiency and light weight mainly in compact panels and portable information terminals. Displaying types for the displays are generally classified into the following types: an active matrix type having an active device such as, for example, an FET and a charge storage capacitor for each pixel, and a passive type having a plurality of electrodes that expand simply in row and column directions, and for forming an image by selecting intersection points thereof to emit light.
In the active matrix type, the FET circuit and the charge storage capacitor are disposed at a positive pole of each pixel, and a voltage applied to each pixel by the stored charge of the capacitor is maintained for a certain period of time. The active matrix type has a system in which each pixel is selected once in one frame of a screen display while luminance information to be displayed is sent thereto, and the same voltage is applied to the organic EL element constituting the pixels constantly during one frame, thereby performing each display. Therefore, in the active matrix type, 100% duty drive is possible. However, there is a problem that the FET circuit constituted of, for example, a TFT, and the capacitor must both be formed on the same substrate, together with each organic EL element.
On the other hand, in the passive type, a plurality of anode electrodes and a plurality of cathode electrodes are formed into strips via an organic EL thin film, in such a way that they cross each other at right angles, thereby preparing a matrix structure in which the luminescence of the organic EL thin film is controlled by the row electrodes and column electrodes at orthogonal points. Since the response speed of an organic EL element is usually 1 xcexcs or less, scanning display due to this matrix structure is possible. The advantage of the passive type is that production costs can be reduced since the configuration of the element is simple and the accuracy of processing is not required as severely as in the active matrix type.
Furthermore, in the passive type, the organic EL thin film element has rectification properties that can adequately suppress crosstalk caused by a current flowing in the opposite direction, and has such characteristics that a high-capacity panel can be driven with a simple drive waveform. For this reason, most of the organic EL element panels in present use utilize the passive type.
FIG. 1 schematically shows a conventional passive type display panel and its control circuit. In a display panel 1, a plurality of strip-shaped anodes 3 made of a transparent electrode material such as indium tin oxide (ITO) are formed in parallel with each other on the surface of a transparent substrate 2. An organic light emitting layer 4 is formed covering the plurality of anodes 3, and on its upper surface, a plurality of strip-shaped cathodes 5 constituted of a metallic thin film are formed in parallel with each other. The anodes 3 and cathodes 5 are usually formed to cross each other at right angles, and the organic light emitting layer at each intersection 6 forms a pixel. In the example shown in FIG. 1, a plurality of pixels of N rowsxc3x97M columns (N=10, M=10) are arranged as matrix elements.
Each of the strip-shaped anodes 3 are connected to a data electrode driving portion 7, and each of the strip-shaped cathodes 5 is connected to a scanning electrode driving portion 8. The data electrode driving portion 7 and scanning electrode driving portion 8 are controlled by a display control portion 9, and the display control portion 9 is controlled by a main control portion 13 for receiving a video signal 30 and controlling the operation of the entire panel.
Light emission processing for one frame period of the display panel is performed in such a way that the scanning electrode driving portion 8 first sequentially selects each cathode 5 in 1 to N (rows) so as to enable each row to be conductive. The luminance of each pixel belonging to each selected row is controlled by the data electrode driving portion 7 by corresponding conduction state of each corresponding row with the signal strength of the video signal 30 by means of 1 to M (columns) of the anodes 3.
However, for a passive type display panel, as shown in FIG. 1, because the electrodes in N rows constituting the matrix are sequentially scanned so that light may be emitted for each row, each pixel emits light only for one selected period among N scannings within one frame period. Thus, in order to obtain the luminance necessary for the display panel by the driving only within a period of a duty ratio (1/N) at which each selected pixel can operate, each organic EL element needs to emit light with a luminance N times as high as the luminance to be actually displayed.
Therefore, due to the driving at such a low duty ratio, the highest luminance of the organic EL element itself must be further enhanced. In addition, when driving current density is increased, to obtain a high luminance, a problem arises that luminous efficiency of the organic EL element is decreased. Further, since it is necessary to, although in an instant, perform driving at high current density, such a problem is caused that current deterioration of the organic EL element is accelerated.
This invention has been achieved in view of the foregoing prior art problems, and the invention relates to a driving method and driving system for an organic EL element panel capable of improving a duty ratio of the prior art. Therefore, one object of this invention is to accomplish a driving method which, in the driving of the organic EL matrix panel based on a multiple line driving method, enables the matrix panel to have a sufficient luminance, without driving the organic EL element in accordance with an inappropriate duty ratio, which improves the reliability of the organic EL element.
According to an embodiment of the present invention, provided is a driving method for a matrix type organic EL element which has a plurality of row direction electrodes and a plurality of column direction electrodes arranged via an organic light emitting layer and which is capable of displaying a predetermined image, the method comprising:
selectively applying an identical scanning voltage amplitude pattern to the plurality of row direction electrodes of two or more rows in accordance with the scanning voltage amplitude pattern applied to the row direction electrodes to simultaneously scan the electrodes;
separately applying a signal voltage pattern, which is applied to the column direction electrodes, to the electrodes simultaneously scanned in the row direction through two or more sets of the plurality of column direction electrodes which are independent of each other; and
simultaneously scanning two or more of a plurality of scanning lines, whereby image information to be displayed in one frame is formed.
Furthermore, the driving method for the organic EL element can be provided which comprises the steps of: integrally forming the two or more adjacent rows of the plurality of row direction electrodes as one set of electrodes; and separately driving by the plurality of column direction electrodes.
Still further, the driving method for the organic EL element can be provided which comprises the step of: providing low-resistance wiring electrodes as auxiliary electrodes connected to each image display portion of the column direction electrodes.
According to an embodiment of the present invention, the present invention can provide a matrix type organic EL apparatus which has a plurality of row direction electrodes and a plurality of column direction electrodes arranged via an organic light emitting layer and which is capable of displaying a predetermined image, and the apparatus has:
means for selectively and simultaneously applying an identical scanning voltage amplitude pattern to the plurality of row direction electrodes of two or more rows; and
two sets or more of the plurality of independent column electrodes for separately applying a signal voltage pattern, which is to be applied to the column direction electrodes, to the row direction electrodes simultaneously scanned in the row direction,
wherein two or more of a plurality of scanning lines are simultaneously scanned, and image information to be displayed in one frame is thereby formed.
Furthermore, the organic EL apparatus can be provided in which the two or more adjacent rows of the plurality of row direction electrodes are integrally formed as one set of row direction electrodes, and the organic EL apparatus can be provided in which low-resistance wiring electrodes are provided as auxiliary electrodes connected to each display portion of the column direction electrodes.